Phonograph pickup cartridge

ABSTRACT

A phonograph pickup cartridge which has a stylus with a pair of driving arms engageable with the ends of a pair of tapered flexible members and formed with tapered openings therein so that the movement of the stylus moves the flexible members and causes the volume of the air chambers therein to vary. A pair of electrostatic transducers are coupled to the cavities of the flexible members and have diaphragms which vary with variations in volume of the flexible members so as to produce audio output signals.

United States Patent [191 Kawakami [111 3,745,263 [4 1 July 10, W73

[ PHONOGRAPH PICKUP CARTRIDGE [76] lnventor: Hirotake Kawakami, 8-3-303 Horino-Uchi l, Suginami-ku, Tokyo, Japan [22] Filed: Dec. 20, 1971 [21] Appl. No.: 209,869

Related U.S. Application Data [63] Continuation-impart of Ser. No. 850,102, Aug. 14,

1969, Pat. NO. 3,649,775.

[52] U.S. Cl. l79/100.41 K, 179/1004] B,

l79/100.4l G

[51] Int. Cl H04r 19/10 [58] Field of Search 179/100.41 G, 100.41 H,

179/l00.4l K, 100.41 V, 100.41

[56] References Cited UNITED STATES PATENTS 3,005,060 10/1961 Weathers 179/1004] K 1,216,946 2/1917 Clement 179/100.41 H

FOREIGN PATENTS OR APPLICATIONS 332,996 8/1930 Great Britain 179/1004] G Primary ExaminerRaymond F. Cardillo, Jr. Attorney-Carlton Hill, .1. Arthur Gross and Marvin Moody et a1.

[57] ABSTRACT A phonograph pickup cartridge which has astylus with a pair of driving arms engageable with the ends of a pair of tapered flexible members and formed with tapered openings therein so that the movement of the stylus moves the flexible members and causes the volume of the air chambers therein to vary. A pair of electrostatic transducers are coupled to the cavities of the flexible members and have diaphragms which vary with varia tions in volume of the flexible members so as to produce audio output signals.

5 Claims, 7 Drawing Figures Patented July 10, 1973 2 Sheets-Shoot 1 Patented July 10, 1973 2 SheetsShoot 8 I PHONDGRAPII lPiCltlUll CARTRIDGE CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 850,102 filed on Aug. 14, 1969 entitled PHONOGRAPl-l PICKUP CARTRIDGE by HIRO- TAKE KAWAKAMI now [1.8. Pat. No. 3,649,775.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates in general to phonograph pickup cartridges and in particular to a novel phonograph pickup cartridge which has low mechanical impedance, is very sensitive and has a wide frequency response.

2. Description of the Prior Art Two general categories of condenser pickups have been known identified as the high frequency bias type and the D.C. bias type. Alhough such pickups are supposed to have excellent frequency response characteristics and low mechanical impedances due to their small moving mass, it has not previously been possible to successfully produce them commercially. High frequency bias type pickups are generally unstable and DC. bias type pickups have exhibited serious frequency limitations due to transducer design difficulties. The output amplifier which is fed by the pickup has high impedance and this requires that the electrostatic capacitance of the transducer be large enough to obtain a good signal to noise ratio. Generally this requires that the diaphragm of the transducer have a large area. This causes an increase in the contact area of the driving member and the diaphragm with mechanically direct coupled systems. The mass of the diaphragm becomes large and the resonant frequency of the cantilevers supporting the stylus falls within the band to be reproduced which results in spurious response. If the thickness of the diaphragm is decreased so as to decrease its mass, multinodal spurious vibrations occur which limit the upper cut-off frequency and deteriorates the frequency response of the pickup.

SUMMARY OF THE INVENTION The phonograph pickup cartridge of the present invention has one or more diaphragms which are not driven mechanically directly by the stylus but the movement of the stylus is mechanically coupled to a flexible member which has an air cavity and causes variations in the air pressure in the flexible chamber. These air pressure variations are coupled to the diaphragm to move the diaphragm and thus changes the capacitance of the pickup. An output cavity is covered by a diaphragm and movement of the diaphragm varies the capacitance between the diaphragm and a second electrode. The output cavity is coupled to the flexible member which has a tapered internal opening and the flexible member terminates adjacent the driving arm of the stylus. The stylus is pivotally supported in the cartridge and has an arm which engages the end wall of the flexible member so as to vary the internal volume of the flexible member thus causing the air pressure within the flexible member and within the output cavity to vary which will consequently procude an audio output in the electrostatic transducer comprising the diaphragm and the second electrode. The cavity within the flexible member is tapered from a small cross-sectional area at the point of contact of the stylus driving arm to a larger cross-sectional area adjacent the output cavity and an acoustical transformer impedance ratio of l to 15 is obtained. In an acoustical transformer of this type the mechanical driving impedance decreases inversely with the square of the ratio of the smaller and larger diaphragms and since the small closed end of the flexible member is the driving point and the output cavity diaphragm is substantially larger, the stylus input driving power may be very low. In a stereo embodiment, the stylus carries a pair of arms mounted at right angles to each other and a pair of flexible driving members are respectively driven by the arms of the stylus and are respectively connected to a pair of output cavities having diaphragms so as to obtain the left and right stereo signals.

Due to the tapered structure of the flexible driving member, a good impedance match is obtained and undesirable standing waves do not occur. Even and smooth frequency response to the pickup results. Very little intermodulation distortion results in the cartridge of the present invention.

Since the spacing between the diaphragm of the elec* trostatic transducer and its second electrode back plate can be made very small, the electrostatic capacitance can be substantially increased and thus the signal-tonoise ratio will be substantially improved.

Since the air column in the flexible member couples the driving arm of the stylus point of the electro mechanical transducer, the relative position of the stylus and the transducer can be varied and the design of the cartridge is facilitated. Permanently polarized dielectric material of so-called ELECTRET may be utilized as the diaphragm of the electrostatic transducer which allows the polarizing voltage source to be eliminated. A field effect transistor and circuit may be incorporated in the cartridge without increasing its weight and size substantially.

An object of this invention is to provide an electrostatic pickup cartridge which has a low efi'ective moving mass and a very high compliance.

Another object of the invention is to provide an electrostatic pickup cartridge which has a wide and linear frequency response.

Another object of this invention is to provide a phonograph pickup cartridge wherein the movement of the stylus is converted into varying air pressure within a tapered flexible member and wherein the air pressure within the flexible member is coupled to a thin output diaphragm.

Yet another object of the invention is to provide a phonograoh pickup cartridge which minimizes external noise and which has a large electrostatic capacitance.

Yet another object is to provide a phonograph pickup cartridge which utilizes an electrostatic transducer that uses ELECTRET as the output diaphragm taken in conjunction with the accompanying drawings although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view illustrating the invention;

FIG. 2 is a sectional view of the cartridge of FIG. 1;

FIG. 3 is a partially sectional view of the cartridge of FIGS. 1 and 2;

FIG. 4 is an exploded view of the cartridge;

FIG. 5 is an exploded view of the electrostatic transducer;

FIG. 6 is an enlarged sectional view of the second electrode taken on line VIVI of FIG. 5; and

FIG. 7 is an enlarged sectional view of the diaphragm and its supporting ring taken on line VII-VII from FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of the phonographic cartridge of this invention and comprises a stylus arm 16 upon which is mounted a stylus 17. The stylus arm 16 is supported in the cartridge 10 which is formed of three main portions including an assembly frame 11 that might be of metal and two plastic members 12 and 13 which mate together and fit in the housing member 11. A support arm 15 extends from the cartridge 10 and is connected to the tone arm of the phonograph and the electrical leads carrying the pickup signals from the cartridge pass-out through the arm 15. A protective cover plate 14 snaps onto the cartridge 10 and has an opening through which the stylus arm 16 extends.

FIGS. 2, 3 and 4 illustrate the internal structure of the cartridge in greater detail. For example, the exploded view of FIG. 4 illustrates the cartridge portion 13 which is formed with a central groove 23 with a central opening 24 into which the stylus arm 16 extends. The stylus arm 16 has a rear portion 18 that is formed with a reduced cross-sectional portion about which a flexible sleeve 19 is moutned. A tip of the rear portion 18 fits into the opening 24 and the stylus arm is supported so as to pivot about the reduced cross-sectional portion which is within the confines of the flexible sleeve 19 for damping. A collar 21 supports a pair of coupling arms and 22 which are mounted at right angles to each other on the stylus arm and respectively move in accordance with the stereo information on a phonograph record being played.

A flexible tapered bellows member 28 is received in tapered mating openings formed in an extension 26 formed on the portion 13. Member 28 has ends 32 and 33 which extend from the portion 26 into the groove 23 and mate with the driving arms 20 and 22 as shown, for example, in FIGS. 2 and 3. The flexible bellows member 28 has a pair of tapered chambers 29 and 31 which have small ends which respectively terminate at the driving points 32 and 33. The rear portion 34 of the flexible bellows member 28 fits over tubular projections 71 and 72 formed in member 12 in groove 27 with which the extension 26 mates. As best shown in FIGS. 2 and 3 the extensions 71 and 72 are formed on a partition 45 with passageways 43 and 46.

The other side of the partition 45 is formed with a pair of depressions in which flexible gaskets 53 and 54 are mounted and a pair of electrostatic transducers 39 and 41 are mounted against the gaskets 54 and 53 and are formed with openings which mate with the openings 46 and 43 so that the transducers communicate with the space within the bellows 31 and 29.

A holding plate 38 engages the ends of the transducers 39 and 41 and is attached as by a set screw to the member 12 so as to lock the transducers to the cartridge.

Transducers 39 and 41 are constructed in the same fashion, and FIGS. 5, 6 and 7 are detailed exploded views of the transducer 41. The transducer 41 comprises a cupshaped electrical conducting member 51 which is formed with an opening 52 which mates with the opening 43 through partition 45. A diaphragm 56 is supported by a metal ring 57 which engages the electrical conducting member 51. Diaphragm 56 comprises a film of suitable plastic material 55 upon which is formed a metallic film 56. The metallic film 56 might be formed by vacuum deposition of aluminum on the film 55. The film 55 and layer 56 comprise an electret diaphragm.

An insulator ring 58 is mounted between the ring 57 and a dishshaped back electrode 61. As best shown in FIG. 6, the back electrode 61 comprises an annular portion 62 of electrical insulating material which has a central electrical conducting insert 64 which is electrically connected to a metallic back electrode layer'63. The back electrode layer 63 might be formed by vacuum deposition of aluminum on the member 61.

A holding ring 66 is externally threaded and mates with internal threads in the cup-shaped member 51 to form an assembled transducer structure. The ring 57 prevents the diaphragm 56 from engaging the end wall of the cup-shaped member 51 and thus pressure variations supplied through the opening 52 from the flexible bellows member 29 will cause the bellows 56 to move relative to the back electrode 63. This variation in movement between the diaphragm 56 and the back electrode 63 will result in a variation in capacitance between these members. Since the diaphragm 56 is electrically connected by the conducting ring 57 to the cupshaped member 51, one electrical output of the electrostatic transducer may be taken from the cup-shaped member 51. The other electrical lead may be connected to the metallic insert member 64 which is electrically connected to the back electrode 63.

Damping material of a suitable fiber as, for example, cotton may be mounted in the bellows members 29 and 31 adjacent the ends thereof so as to provide damping. Damping material 44 and 47 of a suitable fiber may also be mounted in the openings 43 and 46 to provide damping.

The bellows 28 may be formed of rubber or other suitable flexible material. An advantageous feature of this cartridge is that the bellows 28 can be easily replaced by disassembling the carridge portion 13 and inserting a new cartridge portion together with a new stylus holder 16, when desired. Thus, by replacing the stylus and the bellows 28 will result in a cartridge which operates like new. The rear portion 18 may be formed of polypropylene or polyethylene and serves as a fulcrum for movement of the stylus arm. The bellows 28 may be secured to the member 13 by a suitable adhesive. The film 55 may be made of FEP (fluorinated ethylene propylate copolymer) film and the aluminum coating 56 may be formed by vacuum deposition.

It is to be noted that the cross-sectional area of the ends 32 and 33 of the flexible bellows member 28 are much smaller than the area of the diaphragms 56 of transducers 39 and 41. Also, the openngs of legs 29 and 31 of flexible member 28 are tapered and grow larger with distance from the ends 32 and 33. This results in good mechanical coupling characteristics and also eliminates spurious responses caused by reflections. The fiber material inside the openings 43 and 46 and in the ends 32 and 33 provide damping and improve the response characteristics.

A gasket 75 is mounted between the ends of members 29 and 31 and the partition 45.

It is seen that this invention provides a novel phonograph pickup cartridge and although it has been described with respect to preferred embodiments it should not be so limited as changes and modifications may be made therein which are within the full intent and scope as defined by the appended claims.

What I claim is:

1. A phonograph pickup cartridge including:

a stylus supported by said cartridge;

a hollow flexible member mounted in said cartridge 7 and formed with a pair of side-by-side separated fluid-filled hollow tapered driving cavities each formed with small closed first ends that are coupled to said stylus and each formed with larger second ends;

a pair of electrostatic transducers respectively fluidly coupled to the larger second ends of said pair of ta pered driving cavities of said flexible member,

6 wherein said stylus is formed with a pair of driving arms mounted at right angles to each other which respectively engage the first ends of said flexible member, and wherein each of said electrostatic transducers comprise an electrical conductive cup-shaped membr formed with an opening fluidly connected to the respective driving cavity of said flexible member, an electrical conductive diaphragm electrically connected to said cup-shaped member and mounted therein to be driven by pressure variations in the fluid in the associated driving cavity, and a second conductive electrode insulatingly mounted in said cup-shaped member and stationary relative thereto such that movement of said diaphragm produces capacitive variation between said diaphragm and said second conductive electrode. 2. A phonograph pickup cartridge according to claim 1 including fluid damping means mounted in each of said tapered driving cavities of said flexible member.

3. A phonograph pickup cartridge according to claim 1 wherein said electrical conductive diaphragm comprises a flexible plastic film with electrical conductive material attached thereto.

4. A phonograph pickup cartridge according to claim 3 wherein said electrical conductive material is vacuum deposited on said plastic film.

5. A phonograph pickup cartridge according to claim 4 wherein said electrical conductive material is aluminurn. 

1. A phonograph pickup cartridge including: a stylus supported by said cartridge; a hollow flexible member mounted in said cartridge and formed with a pair of side-by-side separated fluid-filled hollow tapered driving cavities each formed with small closed first ends that are coupled to said stylus and each formed with larger second ends; a pair of electrostatic transducers respectively fluidly coupled to the larger second ends of said pair of tapered driving cavities of said flexible member, wherein said stylus is formed with a pair of driving arms mounted at right angles to each other which respectively engage the first ends of said flexible member, and wherein each of said electrostatic transducers comprise an electrical conductive cup-shaped membr formed with an opening fluidly connected to the respective driving cavity of said flexible member, an electrical conductive diaphragm electrically connected to said cup-shaped member and mounted therein to be driven by pressure variations in the fluid in the associated driving cavity, and a second conductive electrode insulatingly mounted in said cup-shaped member and stationary relative thereto such that movement of said diaphragm produces capacitive variation between said diaphragm and said second conductive electrode.
 2. A phonograph pickup cartridge according to claim 1 including fluid damping means mounted in each of said tapered driving cavities of said flexible member.
 3. A phonograph pickup cartridge according to claim 1 wherein said electrical conductive diaphragm comprises a flexible plastic film with electrical conductive material attached thereto.
 4. A phonograph pickup cartridge according to claim 3 wherein said electrical conductive material is vacuum deposited on said plastic film.
 5. A phonograph pickup cartridge according to claim 4 wherein said electrical conductive material is aluminum. 